Selective separation techniques for a target substance based on the structure and characteristics of the target substance is a technique essential for various industries and chemical and biological studies and the like. In the selective separation techniques, a molecular imprinting method is one of the most important methods (e.g., see Non-patent Reference 1). A molecularly imprinted polymer obtained by the molecular imprinting method (to be referred also to as MIP hereinafter) has a characteristic of having a specific binding site complementary to a template molecule, which is effected by the polymerization of a polymerizable molecule having a functional group in the presence of the template molecule and subsequent removal of the template molecule.
As a substitute for a biological antibody, for example, application of MIP to a chromatographic separation of medical substances, a solid phase extraction of environment-derived or organism-derived samples for pretreatment, an artificial antibody for immunoassay and a biosensor device for the detection of structural specificity and the like has so far been examined.
In general, preparation of MIP is carried out making use of an interaction by hydrogen bond in an organic solvent. Thus, it is difficult to prepare an MIP for a water-soluble compound in an organic solvent. Also, when an MIP prepared in an organic solvent is used in an aqueous solution, it poses a problem of reducing its specific binding ability for the template molecule of MIP due to shrinking of the polymer. Further, since water molecule has a characteristic of dissociating hydrogen bond between substances, it is markedly difficult to prepare and use MIP in water. In addition, there is a tendency of causing nonselective adsorption to the surface of polymer matrix in aqueous solution due to a hydrophobic interaction.
In recent years, those which were prepared using acryloyl cyclodextrin and bis-acrylamide (cf. Non-patent Reference 2) and those which were prepared using polyethylene glycol diacrylate by an inter-functional group distance immobilization method (cf. Patent Reference 1), as novel MIPs prepared in an aqueous solution, have been reported. These MIPs show a certain degree of selective adsorption for template molecules.
However, since MIP is produced using excess amount of a functional monomer in the production method of Non-patent Reference 1, it is considered that recognition sites for the template molecule of MIP are not uniform. Also, since MIP is produced by forming an ionic interaction in an organic solvent in the production method of Patent Reference 1, it is considered that the distance between functional groups in the organic solvent is different from the distance between functional groups in aqueous solution. Accordingly, it is considered that the imprint effect is not sufficient by these methods. In addition, these methods have a problem in that they cannot be applied to a water-soluble compound which does not have an aromatic or the like hydrophobic backbone.
By the way, the number of chronic dialysis patients has exceeded 200,000 in recent years; with a tendency of increasing every year. Regardless of the presence of such a large number of chronic renal insufficiency patients, there is no fundamental therapeutic method and it is the present situation that there is only a blood dialysis as a symptomatic therapy aimed at prolonging life. As the blood dialysis therapy for renal insufficiency, it is general to remove uremia related substances and the like toxic substances produced and accumulated in the blood of patients, using a hollow fiber membrane type artificial kidney which uses a cellulose-based natural polymer and polysulfone, methyl polymethacrylate and the like synthetic polymer as the material.
The hollow fiber membrane wall is prepared in such a manner that fine pores having a diameter of approximately from 10 to 100 nm penetrate through it, and the toxic substances are transferred from the blood side to the dialysate side through the pores by the osmotic pressure difference. Currently, performance of the hollow fiber membranes has been markedly improved, thus rendering possible removal of not only urea, creatinine and the like low molecular weight substances (500 daltons or less) but also medium molecular weight substances (500 to 5,000 daltons) or low molecular weight proteins having a molecular weight of 10,000 daltons or more from renal insufficiency patients by dialysis.
However, a hollow fiber membrane capable of removing causal substances having large molecular weights has a tendency that hormones, vitamins, amino acids and water which are essential for the living body are excessively discharged into outside of the body, based on the engineering ground of structure and permeability of the membrane. Accordingly, when the dialysis is carried out for a prolonged period of time, it generates bone and joint disorders, anemia, blood pressure reduction and the like various complications caused thereby.
As described in the above, the current method for treating renal insufficiency by a hollow fiber membrane has many insufficient points in terms of the selective solute-removing ability and has a problem in that the low molecular weight substances essential for the living body are also discharged from the body by the dialysis. However, a countermeasure for this problem of dialysis has not so far been found. In addition, since compulsory time for patients at the hospital is very long in the case of general blood dialysis, there is also a problem in that burden on the social activities is large.    Non-patent Reference 1: B. Sellergren, Molecularly imprinted polymers: man made mimic of antibodies and their application, Elsevier Science (2001)    Non-patent Reference 2: H. Asanuma, T. Akiyama, K. Kajiyama, T. Hishiya and N. Komiyama, Anal. Chim. Acta, 2001, 435, 25    Patent Reference 1: JP-A-2006-137805